The present invention relates generally to the field of switch mode power supply (SMPS). More particularly, embodiments of the present invention relate to SMPS for providing a constant output current for light emitting diode (LED) lighting applications.
Switch mode power supply (SMPS) systems have many advantages over convention linear regulated power supplies. These advantages include smaller volume, better stability, and higher power efficiency. As a result, SMPS has found wide spread applications, such as televisions, set-top boxes, and video recorders, portable telephone chargers, personal digital assistants (PDAs), and even certain automated tooth brushes. In recently years, as light emitting diode (LED) technologies are becoming more prevalent, SMPS is widely used as drivers for LED devices, including in white-light bulb replacement applications.
Unlike convention incandescent light bulbs, LEDs lighting devices do not behave like a purely resistive load in an AC circuit. Therefore, conventional LED light bulbs often do not provide desirable efficiency in the utilization of the AC power supply, which can be measured by “power factor.” As used herein, the power factor of an AC electric power system refers to the ratio of the real power flowing to the load to the apparent power in the circuit. Real power is the capacity of the circuit for performing work in a particular time, and apparent power is the product of the current and voltage of the circuit. A recent U.S. energy efficiency standard requires an LED with greater than 5 W power rating to have a power factor no lower than 0.7. An European standard requires an LED with more than 25 W to have a power factor higher than 0.94.